/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/MeshRefinerBase.h
edge-flip dotproduct metric in range [-1,1] measured between two possibly-not-normalized normal directions. if EdgeFlipTolerance is 0, only the sign of the returned value is valid
double ComputeEdgeFlipMetric ( const FVector3d & Direction0, const FVector3d & Direction1 ) const